Designing robust ground improvement works
GCU designed and detailed a number of the ground improvement works for embankment on weak/soft ground. This includes geotextile reinforcement, partial replacements with surcharge preload, prefabricated vertical drains (PVD) with surcharge preload, stone column at high embankment, stabilisation against pond edge and sinkhole prone areas, complete reclamation of a mining pond and piled embankment.
At embankment areas that has weak subsoil and are prone to ground subsidence due to sinkhole formation, GCU adopted stone columns to treat and improve the foundation soil to a depth of 12 m. In addition, drainage systems and impermeable soil covers were implemented to minimise the infiltration of surface water which are the likely trigger factors to the formation of sinkholes.
At the Sg Langat flood plain, the existing mining pond was reclaimed using complete removal of soft soil at the base and backfilled in layers using compacted suitable fill with the provision of balancing culverts. PVD with surcharge preload was adopted to treat the subsoil at the bridge approaches of this flood plain.
Over at the Sg Labu flood plain, piled embankment and complete replacement were adopted at the bridge approaches. A viaduct was built across the flood plain.
For the first 17 km of the railway line underlain by weak soils up to 20 m and constructed with low or nominal embankment, the track bed below the sub ballast was formed using 2 m to 3 m replacement with competent soil and reinforced with/without geotextile. This was designed using the British Threshold Stress Method to reduce the permanent cumulative plastic deformation of the track bed under the train repetitive loads.
Reinforced concrete (RC) retaining walls were mainly constructed at restricted areas to contain the railway embankment. Pipe and box culverts were used for cross drainage along the entire alignment depending on the location and volume of discharge.
Track drainage in the form of berm drains, toe drains, interceptor drains, and cascading drains were also provided. Baffle chutes were designed to reduce the water speed at certain locations to minimise the formation of hydraulic jumps.
OCL pole foundations in the form of RC driven piles, short bored piles and tube piles were constructed along the alignment. For viaducts, generally bored piles were adopted as the foundation piles. In some places, single large diameter bored piles were designed and constructed.
Soil nails using grid beam system and shotcrete were adopted to stabilise the steep slope at one location. At another location that is close to existing high-rise apartments, contiguous bored pile with reinforced soil wall founded on discrete pile caps with individual piles were constructed top of the CBP wall. The normal cut slopes gradient at greenfield were designed based on geological, subsoil conditions and groundwater profile with varying gradients.
GCU worked closely with SPYTL and other contractors during the design and construction phases. To provide further design and technical support, GCU stationed a team of engineers at the project office to manage and coordinate the design changes during construction.
